Method and apparatus for tundish level control

ABSTRACT

This disclosure relates to a Tundish Level Control System for controlling the level of molten metal in a tundish used on a continuous casting machine. The level of molten metal in the tundish is monitored by a device consisting of a radioactive source and detector unit. Molten metal is supplied to the tundish from a holding furnace disposed above the tundish and which may be tilted to pour metal into the tundish automatically as a function of the level of the metal in the tundish. The holding furnace is preferably rotated or tilted by a screwjack powered by an air motor which is controlled by an operational amplifier and associated control circuitry activated by pulses received from the radioactive detector.

Berry States Pte [191 1 May 20, 1975 METHOD AND APPARATUS FOR TUNDISHLEVEL CONTROL [75] lnventor: Milton E. Berry, Carrollton, Ga.

[73} Assignee: Southwire Company, Carrollton,

[22] Filed: Feb. 22, 1973 [21] Appl. No.: 334,578

[52] U.S. Cl. 164/4; 164/155', 164/278; 222/56 [51] Int. Cl B22d 11/06;B22d 11/10 [58] Field of Search 164/4, 155, 278; 222/56 [56] ReferencesCited UNITED STATES PATENTS 2,433,560 12/1947 Hurley 222/56 3,521,6964/1967 Lowman et a1. 164/155 UX 3,730,254 5/1973 Namy 164/155 X OTHERPUBLICATIONS Cole et 211., Level Control System for Molten Metal in theTundish ofa Continuous Casting Apparatus, Western Electric TechnicalDigest No. 9, January 1968.

Primary Examiner-Robert D. Baldwin Attorney, Agent, or Firm-Van C.Wilks; Herbert M. Hanegan; Stanley L. Tate ABSTRACT This disclosurerelates to a Tundish Level Control System for controlling the level ofmolten metal in a tundish used on a continuous casting machine. Thelevel of molten metal in the tundish is monitored by a device consistingof a radioactive source and detector unit. Molten metal is supplied tothe tundish from a holding furnace disposed above the tundish and whichmay be tilted to pour metal into the tundish automatically as a functionof the level of the metal in the tundish. The holding furnace ispreferably rotated or tilted by a screwjack powered by an air motorwhich is controlled by an operational amplifier and associated controlcircuitry activated by pulses received from the radioactive detector.

13 Claims, 6 Drawing Figures CONTROL CIRCUIT 28 PATENTED MAY 2 0 M5 A Z6 i F n r 1 2 M P m U U y HI 5 N N mm NW m E am 2% ME C mm m 5 R 8 RM WmTN CE E6 E S M P FIG. 28

AIR MOTOR UP 64 AIR MOTOR DOWN RUN R5551 TIMER HOV ' METHOD ANDAPPARATUS FOR TUNDISH LEVEL CONTROL BACKGROUND OF THE INVENTION v Thisdisclosure relates generally to the metal-forming arts, and moreparticularly to a system for controlling the flow of molten metal into acontinuous casting machine adapted for the continuous casting of metalrod.

Wheel-band type continuous casting machines adapted for the continuouscasting rod from molten aluminum and copper are well known in the art.These machines include large steel casting wheels having a castinggroove formed in the periphery thereof and partially closed by anendless metal band defining a mold into which one end thereof the moltenmetal is introduced by means of a pouring spout from the bottom of apour pot or tundish. The molten metal is cooled in the mold and emitstherefrom as a cast metal bar. For normal production operation, it isdesirable to maintain a. constant level of metal in the casting tundish.Generally, a constant metal level in the tundish will produce a constantmetal flow into the mold, thus minimizing the necessity of providingflow control devices in the pouring spout itself.

Although the melting furnace and the casting machine are continuousdevices producing at essentially constant rates, there is always a smalldifference between the output of the melting furnace and the output orproduction rate of the casting machine. Consequently, a holding furnaceis provided between the melting furnace and the tundish to smooth outthese differences and maintain an essentially constant metal flow to thecasting machine. The holding furnace may be either manually orautomatically controlled to pour metal into the tundish and maintain thevolume therein at a constant level.

Heretofore, it has been difficult to maintain a uniform pour rate fromthe holding furnaces presently in use, and also difficult to maintain aconstant level of molten metal in the tundish. Such difficulties havebeen caused by erosion or slag conditions in the pouring vessels, and,when a tilting-type pouring vessel is used, the geometry of the moltenmetal container ordinarily prohibited the use of a'uniform angularmotion in the tilting mechanism of the vessel.

SUMMARY OF THE INVENTION It is, therefore, a primary object of thisinvention to more closely control the molten metal flow into the castinggroove of a continuous casting machine.

More particularly, it is an object of this invention to reduce thedifferences between the melting furnace production rate and the castingmachine production rate in a continuous casting system by monitoring andcontrolling the level of molten metal in the tundish.

Still more particularly, it is an object of this invention I to providea system as above described wherein the level of molten metal in thetundish is maintained by a holding furnace controlled as a function ofthe level of the molten metal in the tundish.

Briefly, these and other objects of the invention that may hereinafterappear are accomplished in accordance with this invention by providing amonitoring system for determining the level of molten metal in thetundish. This monitoring system consists of a radioactive source mountedon one side of the tundish and a detector unit mounted on thediametrically opposite tions thereof cut away for clarity, of thetundish level beam being emitted from the radiation source side of thetundish. Preferably, the radioactive source may be cobalt 60 or otherradioactive materials such as radium or cesium -l37. The radioactivematerial may be either in a rod or a point shape and contained withinsuitably shielded holders mounted on brackets on the outside of thetundish. The holders are preferably leadlined containers equipped with alever-operated shutter to facilitate control of the radiation beamemitted from the source. With the shutter-operating lever in the on"position, a narrow radiation beam will emerge from the front of thecontainer. With the shutteroperating lever in the off position, theradiation beam is blocked by several inches of lead within the shutterstructure and the container then constitutes a safe storage receptaclefor the radiation source.

The detector unit may consist of a scintillation crystal for use with arod source, or multiple scintillation crystals to be used with a pointsource, or Geiger tubes or Geiger-Muller tubes to be used with a pointsource. The detector unit is suitably mounted on the outside of thetundish and is adapted to measure the radiation on the opposite side ofthe tundish.

The radioactive source emits an essentially constant gamma radiation andthe amount of radiation reaching the detector is inversely proportionalto the amount of molten metal contained within the tundish between thesource and the detector. The sourceand the detector are positioned at apreselected elevation with respect to the tundish such that when thelevel of molten metal drops below that elevation, the radiation receivedby the detector will generate voltage pulses at its output which willactivate the circuit of an operational amplifier. The amplifier comparesthe amplitude of the pulses with a standard reference voltage signal andgenerates a control signal to tilt the holding furnace so that it willpour additional metal into the tundish under predetermined conditions.

The holding furnace is mounted for rotation so that it may be tilted bymeans of a screwjack powered by a constant speed air motor. The controlcircuit is programmed such that the air motor will be energized only fora given interval of time, and will then automatically be deenergizedfor'another given interval of time prior to a subsequent interval ofactivation should the level of metal in the tundish still not becorrected to its proper level.

With the above and: other objects in view that may hereinafter appear,the nature of the invention may be more clearly understood by referenceto-the several views illustrated in the attached drawings, the followingdetailed description thereof, and the appended claimed subject matter:

IN THE DRAWINGS FIG. 1 is a fragmentary elevation view, havingporcontrol system of this invention, and illustrates a portion of anopen casting wheel having molten metal delivered thereto through thepouring spout of a tundish, a rotatable holding furnace disposed abovethe tundish,

a gamma ray emitter and detection device positioned in monitoringrelation to the tundish, a control circuit, and an air motor adapted totilt the holding furnace as a function of the metal level in the tundishfor feeding additional metal thereto.

FIGS. 2a and 2b are schematic diagrams of the control circuit of thisinvention, FIG. 2a showing the path of the control signal from thedetector pulse generator through the operational amplifier to thecontrol relays of the furnace-tilting motor, and FIG. 2b showing anassociated circuit which permits intermittent timed control of thefurnace-tilting operation.

FIGS. 3a, 3b and 3c are enlarged vertical sectional views of the tundishof this invention, and illustrate various types of radioactive sourceand detector units that may be usedwith the tundish in accordance withthis invention.

DETAILED DESCRIPTION Referring now to the drawings in detail, there isillustrated in FIG. 1 the tundish level control system of this inventionwhich is designated generally by the numeral 10. The system includes anopen casting wheel 12 having a casting groove 14 formed in the peripherythereof. The casting groove 14, in cooperation with an endless metalband (not shown) defines a mold in the casting wheel 12 into whichmolten metal M is delivered through a pouring spout 16 of a tundish 18.

As discussed above, it is generally desirable to maintain a constantmetal level in the tundish 18 so that the rate of pouring into the moldof the casting wheel 12 I can be maintained at a uniform rate. To thisend, a holding furnace 20 is disposed in juxtaposed relation to thetundish 18 so that molten metal M can be selectively delivered theretothrough an outlet opening 22 of the holding furnace 20. As will behereinafter more clearly described, the holding furnace 20 is mountedfor rotation about a horizontal axis so that it may be tilted to bringthe outlet opening 22 thereof into an open flow condition with respectto the tundish 18. The tilting of the holding furnace 20 is accomplishedby a screwjack assembly 24 which is powered by a constant speed airmotor 26. The air motor 26 is selectively operated by a control circuit28 that is activated in response to electrical signals emitted from aradiation detector unit 30.

The radiation detector unit 30 is mounted on the outside of the tundish18 at a predetermined point diametrically opposite a radiation source 32which is mounted on the other side of the tundish 18. The source 32 maybe any suitable radioactive material such as cobalt 60, radium, orcesium 137.

As seen most clearly in FIGS. 3a, 3b, 3c, the source 32 may be in theform of a rod 34, or a point shape 36. In each case, a suitablelead-lined housing 38 is provided to provide the necessary shielding. Ashutter mechanism (not shown) may be provided to selectively control theamount of gamma rays emitted by the particular source material 32 fromits respective housing 38. The shutter mechanism (not shown), or othersuitable mechanism, is so positioned that the housing 38 will direct thegamma rays through the tundish 18 toward the respective detector unit30.

With further reference to FIGS. 3a, 3b, 3c, the detector unit 30 isselected to be appropriate for the particular source 32 which is beingutilized. For example, when the rod-type source 34 is being used (FIG.3a), the detector unit 30 may be in the form of a scintillation crystal40. When a point source 36 is used as in FIGS. 3b and 3c, the detectorunit 30 may be in the form of either Geiger tubes or Geiger-Muller tubes42 (FIG. 3b), or multiple scintillation crystals 44 (FIG.

3c). In each case, the amount of radiation reaching the respectivedetector unit 30 is inversely proportional to the amount of molten metalM in the tundish 18 disposed between the source 32 and the detector unit30. Consequently, when the level of molten metal M drops below apreselected level, the amount of radiation reaching the detector unit 30will be of a given intensity to activate the control circuit 28 so as tooperate the motor 26 and screwjack assembly 24 to tilt the holdingfurnace 20 sufficiently to supply a given amount of molten metal M tothe tundish 18.

The control circuit 28 is shown schematically in FIGS. 2a and 2b.Radiation passing into the detector unit 30 produces voltage pulses in apulse generator 48 which are applied to an operational amplifier 50 thatis adapted to compare the amplitude of the voltage pulses with apreselected adjustable reference signal, and in response thereto,transmit control signals to the motor 26 through relays 52 or 54 foroperating the screwjack assembly 24 either up or down to tilt theholding furnace 20 as appropriate.

The circuit illustrated in FIG. 2b permits the motor 26 to be energizedonly for predetermined periods of time at given intervals. Thus, whenthe control signal is transmitted by the operational amplifier 50 toeither of the relays 52, 54, switches 56 or 58, which are contacts onthe respective relays 52, 54, will close thereby transmitting thecontrol signal through normally closed timed-to-open contacts 60 or 62and limit switches 64 or 66 to energize the motor 26 in the appropriatedirection. Preferably, the motor 26 is timed to run for l to 10 secondsdepending upon gear ratios and motor speeds. At the expiration of thepredetermined period, the timed-to-open contacts 60 or 62 will open thusdeenergizing the motor 26. The limit switches 64, 66 prevent overtraveland thus assure that the holding furnace 20 will operate only withincertain limits of rotation.

Simultaneous with the closing of the contacts 56 or 58, the controlsignal will also cause a closing of either of contacts 68 or 70. Thus,at the expiration of the predetermined operating period, normally opentimed-toclose contacts 72, 74 will close thereby transmitting thecontrol signal to a RUN relay 76 which will energize a RESET TIMER relay78 that runs for preferably 20 to 90 seconds before resetting thecircuit and thereby permitting a subsequent energizing of the motor 26should the level of molten metal in the tundish 18 still not becorrected to its proper level.

Referring again to FIG. 1, the holding furnace 20 includes a cylindricalrefractory-lined crucible portion 80 that is mounted for rotation abouta horizontal axis disposed parallel to the axis of rotation of castingwheel 12. The molten metal M from a melting furnace (not shown) isintroduced to the interior of the crucible portion 80 through a radialopening 82 closed by a suitable cover or hatch 84 which may be opened bybeing pivoted about a pin 86. The crucible portion 80 is mounted ongenerally U-shaped brackets 88 which are rotatably mounted on supportrollers 90 carried by a structural frame (not shown).

The crucible portion 80 of the holding furnace 20 includes an axiallyextending outlet nozzle 94 having an offset spout portion 96. When theholding furnace 20 is rotated such that the spout portion 96 of theoutlet nozzle 94 is downwardly depending, the molten metal M will bepermitted to flow from the interior of the crucible portion 80, throughthe opening 22 and nozzle 94, downwardly into the tundish 18.

The holding furnace may be rotated or tilted by means of the screwjackassembly 24 which includes a cooperating rotatable screw 100 and nutassembly 102. Consequently, when the motor 26, is energized through thecontrolcircuit 28, the screw 100 will be caused to rotate, therebycausing the nut assembly 102 to translate either up or down thus tiltingthe holding furnace 20 to control pouring of the molten metal Mtherefrom.

In the preferred embodiment of the invention, the motor 26 is a constantspeed air motor that will be energized by the control circuit 28 foronly a certain preset time and will then automatically stop and waitanother preset time before again being energized to tilt the holdingfurnace 20. Consequently, the level of molten metal in the tundish 18will be permitted to stabilize after each incremental pouring of moltenmetal from the holding furnace 20 before the motor 26 is again energizedto further tilt the holding furnace 20 in the event that the level ofmolten metal M in the tundish 18 has not been corrected to its properlevel.

In other embodiments of the invention, a direct current variable speedmotor or a hydraulic cylinder having a widely adjustable hydraulicsupply system may be utilized to tilt the holding furnace 20 in place ofthe constant speed air motor 26. In such embodiments, sufficient controlof tilting of the holding furnace 20 may be obtained without thenecessity of the control circuit 28. It should be understood that thecontrol circuit 28 may be used for any tilting system which uses anessentially constant-speed tilting device such as A.C. electric motors,hydraulic cylinders, and hydraulic motors.

It should be apparent, therefore, that there is provided in accordancewith this invention a novel tundish level control system which enablesthe casting rate of a continuous casting machine to be more closelycontrolled and made more uniform with the rate of production of themelting furnace. The invention makes it possible to maintain a constantlevel of molten level in the tundish 18, and to replenish the supply ofmolten metal in the tundish 18 from a tiltable holding furnace 20 as afunction of the level of metal in the tundish 18 as measured by amonitoring system consisting of a radioactive source and complementarydetector unit.

Although only a preferred embodiment of the invention has beenspecifically illustrated and described herein, it is to be understoodthat further minor modifications may be made therein without departingfrom the spirit of the invention.

I claim:

1. A method of maintaining a predetermined level of molten metal in thetundish of a continuous casting machine by controlling the continuouspouring of molten metal therein from a rotatably mounted holdingfurnace, comprising:

monitoring the level of molten metal in the tundish,

generating a signal in response to said monitoring indicative of saidlevel,

comparing said signal with a reference signal and generating a controlsignal through a control cir cuit in response thereto if said comparisonindicates that said level has deviated from said predetermined level,

rotating said holding furnace in response to said control signal for apredetermined selected interval of time to vary the rate of pouring ofmolten metal therefrom into said tundish, preventing the rotating ofsaid holding furnace subsequent to said selected interval for a giveninterval of time independently of the casting rate, and

thereafter again rotating said holding furnace in response to saidcontrol signal if the level of molten metal in said tundish stilldeviates from said predetermined level,

said steps of rotating and preventing continuing successively until saidlevel reaches said predetermined level.

2. A method as defined in claim 1, wherein said control signal is usedto activate a timer which measures said given interval during whichrotation of said holding furnace is prevented, and resetting the controlcircuit after elapse of said given interval.

3. A method as defined in claim 1, wherein the step of rotating saidholding furnace to vary the rate of pouring includes increasing thehydraulic head of the molten metal in the holding furnace above theoutlet thereof to increase the rate of pouring of the molten metal.

4. A method as defined in claim 1, wherein the step of rotating saidholding furnace to vary the rate of pouring includes decreasing thehydraulic head of the molten metal in the holding furnace above theoutlet 7 thereof to decrease the rate of pouring of the molten metal.

5. A method as defined in claim 1 wherein the step of monitoring thelevel of molten metal in the tundish includes emitting gamma rays from aradioactive source positioned at a selected elevation on one side of thetundish, and detecting the impingement of said rays on a detector unitpositioned on the other side of the tundish as a function of the amountof molten metal in the tundish at the selected level.

6. A method as defined in claim 5 including generating pulses inresponse to the impingement of radiation on the detector, applying thepulses to an operational amplifier, and transmitting a control signalfrom the amplifier through a control circuit to selectively rotate saidholding furnace to supply molten metal to the tundish.

7. In a continuous wheel-band type casting machine for the continuouscasting of molten metal having an arcuate mold defined by a grooveformed in the periphery of the wheel which is partially closed by anendless band, a tundish disposed in juxtaposed relation to the wheel forsupplying molten metal to the mold, a rotatably mounted holding furnacefor supplying molten metal to the tundish, means for monitoring thelevel of molten metal in the tundish, and means responsive to saidmonitoring means for rotating said holding furnace in either directionto control the pouring of molten metal from said holding furnace intosaid tundish during the casting operation; the improvement comprisingcontrol circuit means operatively connected with said monitoring meansand said rotating means for activating said rotating means for at leastone predetermined selected interval when the level of molten metal insaid tundish varies from a predetermined level, said control circuitmeans further including means independent of the casting rate forpreventing the activating of said rotating means for a given intervalafter each of said at least one predetermined selected interval ofactivation said preventing means including timer means for resettingsaid control circuit means after elapse of said given interval.

8. A casting machine as defined in claim 7 wherein said monitoring meansinclude a radioactive source and detector.

9. A casting machine as defined in claim 8 wherein said radioactivesource is a gamma ray emitting rod.

10. A casting machine as defined in claim 8 wherein said radioactivesource is in a point shape and said detector includes multiplescintillation crystals.-

II. A casting machine as defined in claim 7 wherein said means forrotating includes a screwjack assembly powered by a constant speed airmotor.

12. A casting machine as defined in claim 7 wherein said means forrotating said holding furnace includes a motor, said control circuitmeans includes an operational amplifier adapted to compare a signalgenerated by said monitoring means with a standard reference signalindicative of a desired level of molten metal in said tundish. saidamplifier including means for generating a control signal in response tosaid comparison, and

normally closed timed-to-open contacts for transmitting said controlsignal to said motor, said contacts elapse of said given interval.

1. A method of maintaining a predetermined level of molten metal in thetundish of a continuous casting machine by controlling the continuouspouring of molten metal therein from a rotatably mounted holdingfurnace, comprising: monitoring the level of molten metal in thetundish, generating a signal in response to said monitoring indicativeof said level, comparing said signal with a reference signal andgenerating a control signal through a control circuit in responsethereto if said comparison indicates that said level has deviated fromsaid predetermined level, rotating said holding furnace in response tosaid control signal for a predetermined selected interval of time tovary the rate of pouring of molten metal therefrom into said tundish,preventing the rotating of said holding furnace subsequent to saidselected interval for a given interval of time independently of thecasting rate, and thereafter again rotating said holding furnace inresponse to said control signal if the level of molten metal in saidtundish still deviates from said predetermined level, said steps ofrotating and preventing continuing successively until said level reachessaid predetermined level.
 2. A method as defined in claim 1, whereinsaid control signal is used to activate a timer which measures saidgiven interval during which rotation of said holding furnace isprevented, and resetting the control circuit after elapse of said giveninterval.
 3. A method as defined in claim 1, wherein the step ofrotating said holding furnace to vary the rate of pouring includesincreasing the hydraulic head of the molten metal in the holding furnaceabove the outlet thereof to increase the rate of pouring of the moltenmetal.
 4. A method as defined in claim 1, wherein the step of rotatingsaid holding furnace to vary the rate of pouring includes decreasing thehydraulic head of the molten metal in the holding furnace above theoutlet thereof to decrease the rate of pouring of the molten metal.
 5. Amethod as defined in claim 1 wherein the step of monitoring the level ofmolten metal In the tundish includes emitting gamma rays from aradioactive source positioned at a selected elevation on one side of thetundish, and detecting the impingement of said rays on a detector unitpositioned on the other side of the tundish as a function of the amountof molten metal in the tundish at the selected level.
 6. A method asdefined in claim 5 including generating pulses in response to theimpingement of radiation on the detector, applying the pulses to anoperational amplifier, and transmitting a control signal from theamplifier through a control circuit to selectively rotate said holdingfurnace to supply molten metal to the tundish.
 7. In a continuouswheel-band type casting machine for the continuous casting of moltenmetal having an arcuate mold defined by a groove formed in the peripheryof the wheel which is partially closed by an endless band, a tundishdisposed in juxtaposed relation to the wheel for supplying molten metalto the mold, a rotatably mounted holding furnace for supplying moltenmetal to the tundish, means for monitoring the level of molten metal inthe tundish, and means responsive to said monitoring means for rotatingsaid holding furnace in either direction to control the pouring ofmolten metal from said holding furnace into said tundish during thecasting operation; the improvement comprising control circuit meansoperatively connected with said monitoring means and said rotating meansfor activating said rotating means for at least one predeterminedselected interval when the level of molten metal in said tundish variesfrom a predetermined level, said control circuit means further includingmeans independent of the casting rate for preventing the activating ofsaid rotating means for a given interval after each of said at least onepredetermined selected interval of activation said preventing meansincluding timer means for resetting said control circuit means afterelapse of said given interval.
 8. A casting machine as defined in claim7 wherein said monitoring means include a radioactive source anddetector.
 9. A casting machine as defined in claim 8 wherein saidradioactive source is a gamma ray emitting rod.
 10. A casting machine asdefined in claim 8 wherein said radioactive source is in a point shapeand said detector includes multiple scintillation crystals.
 11. Acasting machine as defined in claim 7 wherein said means for rotatingincludes a screwjack assembly powered by a constant speed air motor. 12.A casting machine as defined in claim 7 wherein said means for rotatingsaid holding furnace includes a motor, said control circuit meansincludes an operational amplifier adapted to compare a signal generatedby said monitoring means with a standard reference signal indicative ofa desired level of molten metal in said tundish, said amplifierincluding means for generating a control signal in response to saidcomparison, and normally closed timed-to-open contacts for transmittingsaid control signal to said motor, said contacts being adapted to openupon the expiration of said predetermined selected interval ofactivation.
 13. A casting machine as defined in claim 12 wherein saidpreventing means includes timer means, and said control circuit meansfurther includes normally open timed-to-close contacts for transmittingsaid control signal to said timer means which includes means to closesaid normally closed timed-to-open contacts after elapse of said giveninterval.